High-resolution Doppler images of the spotted contact binary AE Phe

Abstract

We present Doppler images of the short period (P = 0.362 d) W UMa binary AE Phe. In order to obtain the necessary S/N ratio and time resolution required to see individual star-spot features in highly rotationally broadened profiles, we use least-squares deconvolution, which makes use of the information content of the several thousand lines in a typical echelle spectrum. This yields a single rotation profile (free of sidelobes due to blending) per spectrum with a typical S/N ratio of several thousand. We use radial velocity curves, generated from standard profile fitting techniques, to measure velocity amplitudes and the mass ratio. Failure to model star-spots with this method leads to a biased set of values, and we show that an imaging code is essential if accurate system parameters are to be derived. Images are reconstructed from four nights of data which reveal star-spots at most latitudes on both components of the common envelope system. Our model requires that the primary component be several hundred K cooler than the secondary in order to reproduce the profile depth changes with phase. In a two-temperature imaging model, we interpret this as being due to 27 per cent greater - but unresolved - spot filling on the primary relative to the secondary component. The images reveal that dark spots are present on both stars at various latitudes and longitudes. Star-spots are also found in the neck region of both components, which appear to be darker on the side of each star leading in rotation phase - particularly on the secondary component. We investigate the reproducibility of the images from night to night and conclude that the star-spots evolve significantly on very short time-scales, of the order of 1 d. This is significantly faster than the week time-scales found on active single stars and the Sun.